Length Converter

1. 1Type a value into any box — every other unit updates as you type.
2. 2Use the swap button to flip the two headline units.
3. 3Copy any result with the button beside it.
4. 4Adjust the decimal places if you need more or less precision.

All length units are defined against the metre, which since 1983 has been defined by the speed of light. The imperial units are not independent measurements: since the 1959 international yard and pound agreement, the inch is defined as exactly 25.4 millimetres, which makes every other imperial length exact too.

That exactness is why 5 feet 11 inches converts to precisely 1.8034 metres rather than something that drifts in the last digit. The nautical mile is the one unit defined differently — exactly 1,852 metres, chosen to approximate one minute of latitude.

Conversion works by taking your value to a single base unit and then out again, so every pair of units is consistent with every other. Values are calculated at full double precision and only rounded for display, which means round-tripping a number through two conversions returns what you started with.

Converting a height of 5 ft 11 in to metres

1. 5 ft 11 in = 71 inches
2. 71 × 0.0254 = 1.8034

Result: 1.8034 metres, or 180.34 centimetres.